Running multiple times generates many duplicate folders named by run date

[bhazelton]

This is not what I expected. I see now in the docs that this is the default if you don't set the description option to something. I think this is the wrong default because it leads to massive data duplication. I'm fine with this being an option, but you should have to opt in to this behavior. The default should be to require a name (currently passed via the description yaml entry).

Edit: I had originally thought this might be related to the checkpointing issue (#66), but I added a description, so now I only have one folder and I still cannot get checkpointing to work.